The present invention relates to a governor for generating a governor pressure adapted to switch a shift valve of an automatic transmission by the rotation of a flyweight and, more particularly, to a governor in which no governor pressure is generated until a governor rotational speed increases to a predetermined breakpoint speed, and when the governor speed has reached the breakpoint, the governor pressure is raised in a stepwise manner in which, the governor pressure increases in accordance with the governor speed.
Hitherto, as such a governor, the governor disclosed in U.S. Pat. No. 2,762,384 has been known.
The governor disclosed in U.S. Pat. No. 2,762,384 has a sleeve engaged with the gear of an output rotation transfer portion of an automatic transmission, and a spool, which is slidable in the axial direction, is provided in the sleeve. A pair of flyweights which generate centrifugal forces during the rotation of the sleeve and are exposed to the outside are attached on the end opposite to the end formed with a gear. When the sleeve rotates, the flyweights swing in a manner in which they are swung outwardly from a pin serving as a rotational center and in dependence on the centrifugal force, thereby depressing the spool. When the spool is depressed, an opening degree of the valve portion, which places the entrance port and exit port formed in the sleeve in communication, increases. Since a constant line hydraulic pressure is supplied from the oil pump to the entrance port, the governor hydraulic pressure corresponding to the opening degree of the valve due to the depression of the spool is generated in the exit port, so that the governor hydraulic pressure rises with an increase in governor speed.
In the conventional governor, the governor pressure is generated simultaneously with the start of the rotation of the sleeve and thereafter, the governor pressure is also sequentially increased in association with an increase in sleeve speed. However some vehicles require that the switching operation of the shift valve can be inhibited until the vehicle velocity reaches a predetermined speed. For this purpose, it is necessary that no governor pressure is generated until the sleeve speed reaches a predetermined speed, namely, a breakpoint.
A known governor having breakpoint, a is disclosed in U.S. Pat. No. 3,431,929.
In U.S. Pat. No. 3,431,929, a spring is disposed between a pair of flyweights which are slidably attached by a pin, the spring adapted to suppress the extension of the flyweights due to the centrifugal forces and attached to the edge of the sleeve.
Therefore, the motion of the flyweights is restricted by the spring until the sleeve speed reaches a rotational speed corresponds to the breakpoint. When the sleeve speed reaches the breakpoint, the centrifugal forces of the flyweights overcome the spring force and press and bend it in a snap action manner. Thus, the ends of the flyweights come into contact with the edge of the spool to thereby start depressing the sleeve. At this time, the governor pressure increases in a stepwise manner.
However, in the foregoing governor having a breakpoint, there is a difference between the breakpoint when the sleeve speed was raised and the breakpoint when it was lowered after that, so that there is a problem in that the breakpoint cannot be accurately set.
In addition, since the spring for establishing a breakpoint is provided for the flyweights, the spring force exerts an influence on the generation of the governor pressure corresponding to the rotational speed after the breakpoint is exceeded. Therefore, there is a problem in that the foregoing governor cannot be used at a very high rotational speed.